The United States was said to be considering airstrikes aimed at eliminating individual leaders of Isis (Islamic State) as Turkey came under mounting pressure to stem the flow of jihadists across its border into Syria.
As Washington debated extending airstrikes into Syria, senior British politicians said Ankara should act immediately to block foreign recruits from entering Syria via Turkey, en route to joining Isis. This weekend large numbers of Isis jihadists were trying to secure the border area, pushing northwards in armoured trucks looted from abandoned Iraqi military bases.
Isis wants to establish control to make it easier for potential recruits to gain safe passage and allow in supplies of weapons and oil. The route is used by foreign fighters.
US officials said yesterday there was a "new context" for confronting Isis - and cutting off supply routes - following the beheading of US journalist James Foley. In a sign that Washington may widen the field of its airstrikes, the White House said it was ready to "take action" against any threat to America in Iraq or Syria.
Deputy national security adviser Ben Rhodes said a strategy to deal with extremists had to take in "both sides of the border, Iraq and Syria", adding: "If we see plotting against Americans, we see a threat to the US emanating from anywhere, we stand ready to take action against that threat. We've made it very clear time and again that if you come after Americans, we're going to come after you wherever you are, and that's what's going to guide our planning in the days to come."
According to US military officials cited in the Wall Street Journal and New York Times, the time needed to carry out strikes at high-value targets, such as individual leaders, could be "an hour, it could be a week". Officials said they were examining the possibility of strikes by fighter jets and bombers as well as sending special forces into Syria.
Isis declared itself a "caliphate" in late June and has since added large parts of northern Iraq to territory it already held in eastern Syria.
President Barack Obama authorised air raids in Iraq two weeks ago to help regional Kurdish and Iraqi forces fighting Isis in the country's north. If Washington widened its attacks to extremists in Syria it would mark a turning point, ending its hands-off approach to the civil war.
EU countries have been exerting pressure on Turkey to do more to seal its border for weeks. Because Ankara has wanted to oust President Bashar al-Assad in Syria, Turkey has kept its border open to jihadists, including Isis fighters, allowing the area to become a safe haven over the past three years. While the Turks say Isis is no longer welcome, it has not sent in troops in large numbers to man the border.
The British Foreign Secretary, Philip Hammond, has not explicitly ruled out supporting a policy of US airstrikes but sources say there is no prospect of Britain taking part.
Yesterday, the UN called for a concerted effort to end the siege of Amerli, a town 177km north of Baghdad which is encircled by Isis jihadists. The town is home to 18,000 Shia Turkmen. As Shia, they are directly targeted by supporters of Isis, who consider them apostates.